Grapes (Vitis vinifera) have been used as a model system for understanding ripening and ripening-related physiological disorders in fleshy fruit; hence, a comparative analysis was undertaken to explore the mechanistic basis of a paradoxical ripening phenomenon of grape berries known as suppression of uniform ripening (SOUR) shrivel. Fruit organoleptic attributes coupled with morphology and structure, and tissue organization in various organs of healthy and afflicted field-grown grapevines were examined using a range of microscopy techniques. As opposed to healthy berries, SOUR shrivel berries were flaccid and had the lowest pH and lowest levels of sugars, potassium (K), and malic acid that paralleled with a significant reduction in the synthesis of anthocyanin. On the other hand, titratable acidity, tartaric acids, and tannins were much higher than perfectly healthy berries. The SOUR shrivel cluster tinged its rachis red but held no relationship with flaccidity of the berries because healthy vines totally devoid of SOUR shrivel clusters also displayed same coloration. Furthermore, although the phloem sieve tubes in both cases were plugged with callose, a carbohydrate generally implicated in impeding translocation in phloem, the afflicted grapevines exhibited relatively more plugged sieve tubes. The study revealed that the spatiotemporal configuration of cell and tissue communities determining the structure–function relationship remained intact in afflicted vines throughout the growing season. However, the functionality, especially of flows in phloem sieve tubes, started to decelerate after veraison (initiation of ripening) most likely as a result of early activation of callose synthesis and subsequently plugging of sieve plates during the remaining course of ripening. Hence, in future studies, a broader analysis of phloem sieve tubes entailing its flows and ultrastructure in phloem-girdled grapevines simulating symptoms of SOUR shrivel is needed to characterize the mechanistic basis of SOUR shrivel.
Bhaskar R. Bondada
Drift hazards and the effects of 2,4-dichlorophenoxy acetic acid (2,4-D) spray drift on woody perennials have been commonly observed since its discovery in the 1940s; however, 2,4-D-induced phytotoxicity, morphogenesis, and structural and compositional anomalies of their vegetative and reproductive structures are not well understood. Healthy and 2,4-D-injured shoots of grapevine (Vitis vinifera L.) from a commercial vineyard experiencing persistent drift were compared. The morphoanatomy of healthy and 2,4-D-injured leaves and berries were examined using light and scanning electron microscopy (SEM). Along with the microscopic examinations, stomatal conductance (g S), leaf growth characteristics, and mineral composition were also determined. The morphoanatomy of healthy leaves resembled that of a typical angiospermic leaf. By contrast, shoots exposed to 2,4-D phytotoxicity displayed epinastic behavior and developed grotesquely malformed leaves that were thick, fan-shaped, enated, and interveinally puckered as a result of fasciation of veins. The cellular architecture, including the vascular bundles, was altered as a result of the formation of parenchymatous replacement tissues. The g S, leaf index, leaf area, and petiole dimensions were significantly reduced in the 2,4-D-injured leaves. 2,4-D-injured leaves; however, accumulated high levels of nitrogen, potassium, and iron compared with healthy leaves. The clusters (fertilized inflorescences) of the injured shoots developed epinastic curvature and predominantly bore live green ovaries (seedless unripened pseudofruit) instead of true berries (fertilized fully ripened fleshy fruit). These abnormalities are expected to severely perturb the vital functions of photosynthesis and transpiration as evidenced by low g S and poor fruit set leading to senescence and localized necrosis ultimately causing death of current-season shoots.
Bhaskar Bondada and Markus Keller
Berry shrivel, a physiological disorder, adversely affects ripening of grape (Vitis vinifera L.) berries; however, its causes are unknown. We adopted a holistic approach to elucidate symptomatology, morphoanatomy, and osmotic behavior of grape berry shrivel. Berries from healthy and afflicted vines were analyzed compositionally and with various techniques of microscopy. Healthy berries developed all physical and compositional attributes desirable for wine-making. Conversely, berry shrivel berries were grossly metamorphosed manifested as shriveling of the pericarp, which paralleled with loss of membrane competence in the mesocarp cells causing its collapse and a loss of brush. The most intriguing observation was the presence of non-druse crystals. These berries had high osmotic potential (ψS) as a result of low accumulations of sugar and potassium. Nonetheless, the seed morphology, structure, and viability were similar to healthy seeds. Berry shrivel grotesquely modified grape berries both compositionally and structurally, which was paralleled by their inability to accumulate sugars followed by cell death in the mesocarp. Although the mechanisms of berry shrivel remain uncertain, our study provides valuable background information for generating suitable guidelines to minimize the incidences of berry shrivel and also to design future studies toward unraveling the mechanistic basis of berry shrivel.
Bhaskar Bondada, Peter D. Petracek, and Jim Syvertsen
Recent interest in reducing nitrate levels in ground water has stimulated the re-examination of foliar application of urea on citrus trees. Because the cuticle is the primary barrier to foliar uptake, we examined the diffusion of 14C-urea through isolated citrus leaf cuticles. Cuticles were enzymatically isolated from leaves of the four youngest nodes (1 month to 1 year old) of pesticide-free grapefruit trees. The diffusion system consisted of a cuticle mounted on a receiver cell containing stirred buffer solution. Urea (1 μL) was pipetted onto the cuticular surface, and buffer solution was sampled periodically through the side portal of the receiver cell. The time course of urea diffusion was characterized by lag (time to initial penetration), quasi-linear (maximum penetration rate), and plateau (total penetration) phases. Apparent drying time was less than 30 min. Average lag time was about 10 min. The maximum penetration rate occurred about 40 min after droplet application and was about 2% of the amount applied per hour. Rewetting stimulated further penetration. The total penetration averaged about 35% and tended to decrease with leaf age. Dewaxing the second node cuticles by solvent extraction significantly increased maximum penetration rates (30% of the amount applied per hour) and total penetration (64%).